It depends on who it is.
There is a couple we travel with to Vegas who also own a timeshare. They understand there is a cost with timeshares, since they have their own, so they offer to pay for our tickets to shows (as a foursome we usually do 2 or 3 shows in a week) which usually exceeds $500. This is fair enough to me and then we split dinners down the middle, and pay our own way for any daytime excursions.
I have taken family in the past (middle aged adults) who completely abused the privilege and were even borderline ungrateful. The last straw was when the parents (of a family of 4) took their luggage into the second bedroom and immediately threw the second queen sized mattress from the bedroom for their teenage kids to sleep on in THE LIVING ROOM. So I had to deal with their kids taking over the living area and we couldn't really use it as a living room, it was like an open bedroom and there was no where to walk. Really trashy of them in my opinion. They were my husbands relations and he asked me not to make a big deal out of it. The parents haven't been invited back. PS I paid for everything and I mean everything on that trip. So that was the end of Mrs. Nice guy. I would never take people older than my age, friend or family, without clear expectations. I am not asking for much, a few dinners or excursions would be appreciated since I am housing you for a week in paradise.
Their son has come with on vacations since then (he is now 25+) and my child (21) and her friends or boyfriend come frequently too. Since they are all adults and they all work I insist they have a stake in it. They pay their own airfare and I ask that they each pay for one dinner for everyone and I pick up the rest for the week (usually the most expensive ones, naturally). I pay for the excursions I plan but any extra stuff like drinking in the evenings, or windsurfing, tours or whatever else they want to do on their own without the old folks, they pay. It's still a good deal for them because they get free room and board basically. They couldn't afford to go without me, so they love it. They want to know where we're going to go next when we are at the airport flying home.